


Bark Side of the Moon

by snasational



Series: Classic Vs The Multiverse [3]
Category: Undertale (Video Game)
Genre: M/M, Master/Pet, Pet Play, Skull Fucking, Underfell Sans (Undertale), Vaginal Sex
Language: English
Status: Completed
Published: 2020-12-23
Updated: 2020-12-23
Packaged: 2021-03-10 17:48:45
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,502
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28271169
Author URL: https://archiveofourown.org/users/snasational/pseuds/snasational
Summary: “I found the collar.”Red grins lecherously to hide the growing nervousness. “Oh? Did ya now?”
Relationships: Sans/Sans (Undertale)
Series: Classic Vs The Multiverse [3]
Series URL: https://archiveofourown.org/series/2065212
Comments: 3
Kudos: 107





	Bark Side of the Moon

**Author's Note:**

> it's been a few days, sorry about that!
> 
> I have never written pet play before. I hope it wasn't too awkward. 
> 
> Not beta'd or proofread

The collar is nothing special. A simple blue with no designs or ornaments. Not even a tag, just a place for a leash to be clipped onto it. At first, Red didn’t like it. He scrolled right past the thing without another thought. But, the more he looked the less Red liked any other options. Nothing seemed really...classic-ish. 

To Red, collars were important. If it didn’t scream a person’s name, that person should not be wearing it. Finding the right collar was imperative. He thought back to his lover, and the way he acted and dressed. Plain and unassuming with underlying charm. 

The blue collar came to mind and Red wanted to wack himself in the head. Of course! He should’ve known that Classic didn’t need bedazzlement and looking for anything that had a design like that was a waste of time. He purchased it without a second thought and shoved it under the bed when it finally arrived. 

Buying the collar was one thing, getting Classic to wear it was another. He was a normally laid back dude and rarely had any opinions to share. Red doesn’t think Classic has ever so much as given his own collar more than a glance. There was no obvious interest but on the same coin Classic has never seemed disinterested by it. 

For well over a month, Red tried to plot on how he’d subtly go about asking. Usually, he’d ask bluntly how his partner would feel about wearing it. Back where he’s from it’s so common that you don’t even really  _ need  _ to ask. Approaching Classic requires much more couth. And Red is more than capable of doing so. 

They get shitface drunk together, as they normally do on a Saturday night. There’s a lot of random chatter, things they’ll forget about in the morning and never talk about again. After that, there’s a couple rounds of fucking and off to bed they are with water and Aspirin waiting for them in the mornings. Their routine is safe and secure.

Red would love to see that pretty little neck of his claimed. That bare bone is tantalizing. He wants to hide it from the world so that nobody but Red may look at it. It sounds possessive, but in reality it’s just the way things work for him. No malicious thought or intent behind it. 

Tonight, Classic is acting strange. More mumbling, less jokes, and a whole lot of awkward silences. Red is about ready to call it a night without their usual fuck session, but Classic opens his mouth and says both the worst and best possible thing. 

“I found the collar.”

Red grins lecherously to hide the growing nervousness. “Oh? Did ya now?”

Classic nods. “Was lookin’ for that toy you used on Blue the other night. Thought it might’ve been under the bed.” He chuckles but there’s an edge to it. “At first, I figured it was another one for you. And then I realized you only have one collar, and that you don’t wear blue.” 

Red hums. He leans against the railing of their house’s balcony and circles his finger over the rim of his solo cup. “Yeah? And what did ya think?”

Classic blushes, but regardless he looks his counterpart dead in the eyes. “I have never done anything kinkier than changing the shape of my dick.” He says honestly. But he pauses and glances away from Red’s. He trains them off in the distance, where both of their Frisks are running around and throwing snowballs at each other. 

Normally it’d be a cute sight. He’d even gloat about how his kid could totally beat Classic’s kid’s ass. Even if that’s a definite lie, because his Frisk cried when they stepped on Doomfanger’s tail one time. Still, Red would defend their honor. But this is not a normal situation and he needs Classic to focus on him again. 

“I hear a ‘but’.”

Classic looks at him again. “...I don’t hate the idea of acting like a dog every once in a while, I guess.” 

What. 

Red gawks at him.

“Emphasizing the every once in a while bit, by the way.”

Red cannot believe that this is happening. Pet play? Sure, he’s no stranger to it, but that was the last thing on his mind when he bought the collar. It’s so bizarre that Red starts laughing. It’s a genuine one and it causes Classic to flush a darker color. 

“Hah! Oh my  _ god.  _ I ain’t laughin’ at you, Sugar. But...holy shit I was not expecting that!” 

“Mmkay. Forget I said anything.” The permanent grin makes it hard for them to look upset, but Classic manages to pull it off by radiating displeasure. 

Red is quick to try and make amends. “Aw, don’t be like that. If ya really wanna try it out then we can. I didn’t buy the damned thing for that, though.” He wipes a stray tear from his eye socket. Man, he hasn’t cried laughter tears in a long time. 

Classic shifts to something more mortified, and then he looks apprehensive. “What did you buy it for then?” 

“I just wanted people to know that ya were taken, that’s all.”

This is new territory for the both of them. They’ve never even talked about relationships before, and even when they bring Blue into their bed there’s no discussion of boundaries. Although, some things simply do not need to be spoken out loud. Red loves Classic, and Classic loves Red. There was no need to say it beforehand. 

“...Oh.”

“However, now that ya mention it, I definitely want ya on all fours actin’ like an animal for me.” Red chuckles again, the tone much heavier than his earlier guffaws. He’s envisioning all the different ways this could play out, all the positions he could fuck Classic in while he’s forced to take it like a champ. 

Classic frowns. He’s back to watching the kids. They’re building snowmen now. One of them looks suspiciously like Boss. He’s sure his brother will fawn over it later. 

“You’re so perverted.” Classic grunts. He’s not rejecting the fantasy, so Red takes this as a good sign.

“Yeah, I know.” 

*

“What’s the safe word?”

Classic is on his knees, his palms pressed flat to the ground. Like a sitting dog, he thinks gleefully. From the waist below, a deep blue ecto body glows, already summoned for the convenience of Red. He’s even conjured a floppy pair of ears and a tail reminiscent of a Bernese Mountain dog. Red saves that information for later. He never thought Classic would have a favorite dog breed, considering his brother’s well known hatred for them.

The skeleton is stripped bare aside from the collar that now adornes his neck. Just the sight of it has Red seeing hearts. Knowing that he finally managed to get him to wear one fills him with a bone deep satisfaction. 

Red sits on the couch a couple of feet in front of him. 

“Mustard.” 

Red’s smile twists into something sinister. “Good boy.” 

“Red,” Classic whines. He can’t finish his sentence because Red tugs on the leash that’s connected to Classic’s collar. He yelps at the movement, his body jerking. 

“That don’t sound much like a dog to me.” 

Classic turns so blue that it’s almost concerning. He shifts on his knees and readjusts his palms on the floor. His mouth stays firmly shut, embarrassment evident with every move he makes. That just won’t do. 

“Come on, puppy. You’ve been such a good boy, lemme hear that bark of yours.” He tugs the leash again and Classic has no choice but to shuffle forward on all fours. Once he’s close enough, Red rests a gentle hand on top of his skull and strokes it encouragingly. 

“A-arf?” 

Red has to try not to laugh for the sake of his partner. “Come on, ya can do better than that.” He moves his strokes to the back of Classic’s cranium. He leans into the touch ever so slightly. 

Classic averts eye contact. “...Arf.” 

Yeah, they’re definitely going to have to work on that. Red grabs him by the jaw and forces him to look at Red again. “Don’t ya dare look away from me.” He hisses. “Bad boy.”

Classic squirms. And then in a surprisingly bold move, he turns his head and licks the phalange closest to his mouth. It’s an apology, he realizes. Red sucks in a breath. Maybe this whole evening  _ isn’t  _ going to be some embarassing experiment in their sex life that they try desperatley to forget in the future.

Pleased, Red scratches one of the ears that were conjured earlier. “Atta boy.”

Classic’s grin twitches, the uncomfortableness morphing away into amusement. This time, he whines low like a dog begging for attention. He inches even closer and licks the groove where Red’s tibia meets his patella. The skeleton laps the bone with lazy, affectionate strokes. Red sighs contently, enjoying the feeling of tongue against bone.

“How cute.” Red cooes, massaging those fluffy little ears more vigorously. “Such a good puppy. Back off for a second, baby boy.” 

Reluctantly, Classic scoots back. Red lets go of his ears to shimmy his way out of his shorts, revealing a twitching erection. Classic stares at it with a heated look, lust blurring the edges of his eyelights. 

“Ya can come back now and show ya master how much ya appreciate him.” Red orders. Classic blinks out of the daze he was in. Red is about to give another, much more harsher command, but all at once the other is on him. There is no finesse to it, Classic slurps on his cock like he’s a starved animal.

Red isn’t expecting it. Classic never does anything with urgency, not even blowjobs. It forces a groan out of him. 

“Holy shit, Sugar.” He huffs, yanking on the leash and urging him. Classic’s hands fly up and grip onto the edge of the couch. Big eyelights that remind him of Blue look up at them, the hazy quality concerning him at first. He seems so into this scenario, when just a few moments ago he was basically shaking with anxiety and embarrassment.

Classic is certainly an enigma. Red’s okay with that, it makes him all the more appealing.

“Good boy, such a good boy, why don’t ya take me in your mouth? Come on, open that pretty little mouth of yours.” 

Classic obeys his command and unhinges his jaw even wider, allowing enough space for Red to ease his cock into his skull. Skull fucking is not a new thing for them, but usually it’s Red on the receiving end. He’s always had a thing for giving head, but receiving it is just as nice. He ought to do this more often. 

Magic swirls around inside Classic’s mouth, providing suction that’s otherworldly. You wouldn’t be able to get this from any other species of monster, that's for damn sure. Classic makes a muffled noise over his cock which causes a nice vibration to spread through it. Red shudders at the sensation. 

“God fucking-!” He can’t hold back anymore. He rolls up the leash until it’s wrapped all around his hand. Red has to hunch a bit to make it work, but the desired outcome makes the slight pressure on his spine well worth it. By doing this he’s able to yank Classic’s skull as close to Red’s pelvis as possible. 

The first time he does this, Classic flinches and struggles. When Red keeps holding him down, he untenses and allows his master to do as he pleases. Now that his cock is firmly down Classic’s throat, he fucks up into it with short and harsh thrusts. 

Classic takes it like a champ. He holds perfectly still, being used as nothing more than a toy for Red’s pleasure. It suits Classic because he’s not usually active in any manner, including the bedroom. A true pillow princess if Red ever saw one. Luckily for him, Red gets a kick out of taking care of everything. Having to put in work to make Classic cums always ends up giving him the ultimate sense of validation.

“You’re always the best for me, sugar, And now look at ya. I claimed ya, ya hear me? You’re  _ mine.”  _ The more he talks the rougher his thrusts get. Classic is clawing at the couch now, but he makes no move to stop what’s happening. “Everyone is gunna see that collar and know who you belong to.”

It’s euphoric. To be in control, to be the owner instead of the owned. And most importantly, knowing that Classic trusts him enough with something like this makes the experience so much better. 

“Ngh, oh fuck! Come on puppy, get ready to drink your milk, cause it’s coming fa-Oh, oh! Yeah, swirl your tongue like that, I- Shit!” He cums hard down Classic’s throat. 

Red doesn’t let Classic back up until he’s swallowed every last drop of his release. And he does so without complaint. With how much they fuck, Classic is definitely used to the taste of jizz by now. When he’s pulled off, nobody is surprised to see that Red is still hard. He can go for another round no problem, his stamina far better than Classic’s.

Red unwinds the leash and slumps down onto the couch. “You did such a good job.” He praises earnestly. “Get up on my lap, a good puppy deserves a treat.” 

He doesn’t need to tell him twice. Classic clammers up onto Red’s femurs and grips tightly onto his shoulders. Behind him, the magic tail wags with excitement. Red chuckles at the eagerness. You wouldn’t catch Classic dead acting like this outside of the bedroom. He is immensely glad that he’s one of the few who gets to see him in this state. 

Red grips onto Classic’s hips and eases him down onto his cock. “Easy goes it, ain’t no rush.”

Classic seems to disagree. He huffs and shoves his hips down, taking him all in one go. And then he’s bouncing, riding dick like Red’s never seen before. Their sexes are nothing more than a blur of blue and red. He’s taking him fast and hard, using him like how Red used him earlier. Red murmurs encouragement and praises in his ear-canal. 

He quite obviously doesn't last all that long. As a matter of fact, neither of them do. Red can safely say he’s never came at the same time before, but the sensation is unique. The squeeze and clench of Classic’s cunt milks him for all he’s worth. It pumps his pussy full of his seed, and because of the spasms in his pussy the jizz is pushed right back out. 

It’s a mess. 

Red couldn’t be any happier about it. 

…

…

…

…

“Sooo, when can we do that again Sugar?”

“...”

“Aw, don’t be like that!” 

Classic flicks him in the face and rolls over. Despite all that, the plain collar still sits around his neck. 

**Author's Note:**

> Comments and Kudos are always appreciated! 
> 
> come chat with me over on twitter @ snasational


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